Potentiometer



J l 28, 1964 J. CLAYTON, JR 3,142,312

POTENTIOMETER Filed Jan. 14, 1965 2 Sheets-Sheet 1 INVENTOR.

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44 50 Ja/W6WJZE July 28, 1964 Filed Jan. 14, 1963 J. CLAYTON, JR 2POTENTIOMETER 2 Sheets-Sheet 2 INVENTOR.

M, Mi?! United States Patent 3,142,812 POTENTIOMETER John Clayton, In,Maynard, Mass, assignor to Waters The present invention relates tootentiometers and more particularly to precision rotary Potentiometers.

It is the principal object of the invention to provide an improvedpotentiometer construction which allows the manufacture and maintenanceof a minimum inventory of sub-assemblies and'allows a maximum amount ofinterchangeability of components, without adding substantially to thecomplexity, and thus without impairing the full economic advantage ofthe universal type of construction. Rotary potentiometers are employedin a wide variety of types of uses and have a correspondingly widevariety of external construction details, a full line of even a singlesize, ohmic value, temperature characteristic, etc., including a varietyof combinations of external drives (ordinary shafts of various lengths,terminating in various forms of coupling shapes for operation by tools,motors, knobs, etc., and also worm drives, dial-type drives and others)and other mechanical variations (threaded bushings of variousdimensions, locking or non-locking, servo and other types having nobushing, calibrated exteriors, etc.). All of these variations preventthe manufacture and distribution of precision rotary potentiometers atcosts comparable to those which would prevail if the volume ofdistribution were not divided, because of these variations, into a largenumber of fragments, each constituting a separate item as regardsmanufacture and distribution. Various structures have been devised topermit the construction of rotary potentiometers of a variety ofmechanical types and configurations by assembly from more or lessinterchangeable parts, but the provisions for interchangeability oruniversality have in general defeated their own purpose by being ofexcessive cost, particularly when miniaturized.

It, is a further object of the invention to provide a lowcoststandardized base, resistance element, and wiper assembly for use in avariety of external potentiometer constructions, which allows a maximumamount of flexibility in the final assembly of the otentiometers, andwhich may I be stored as a unit. In accordance with the invention, thisassembly is installed in a simple and novel manner in a variety of typesof fronts of varying configuration, and

with various types of drive members.

In any pre-assembled construction designed for the attachment of shaftsor similar drive members to the rotating wiper, arrangement must be madefor keying of the wiper assembly to the drive members. In the presentconstruction, the added fabrication cost of providing such keying isrecouped in a novel manner by utilizing the necessity for a coupling atthis point to permit the elimination of the complex constructionsnormally required in .insulating the wiper from its axial support; inthe present construction, an insulating member is inserted in thecoupling between the external operating or drive member and the wiperassembly, the entire rotatable drive assembly being constructed ofeasily fabricated metal conductors, and being rotatably mounted on anaxial conducting terminal member extending through the insulating base,which thus serves as an internal rotational bearing and an ex- .ternalwiper connection, eliminating the necessity for any separate bearingstructure and for any wiper take-off in the nature of a slip-ring,beyond the electrical contact at the bearing interface.

The insertion of the insulator in the coupling between the wiper and theexternal drive may be further utilized to 3,142,812 Patented July 28,1964 eliminate other parts and assembly operations, as will be betterunderstood from the description of the embodiments of the inventionshown in the drawing. The elimination of parts and assembly operationsis of particular advantage in the case of subminiature potentiometers(diameter less than inch) because of the extreme precision ofmanufacture and assembly which is required to produce suchpotentiometers by mere scaling-down of dimensions of constructionsheretofore known.

In one form of front applied to the base assembly to be described, inaccordance with further novel teachings of the invention, there isprovided to manipulate the wiper assembly a manually or otherwiserotatable surface disc covering the front face of the stationary portionof this front assembly. This disc has a window or viewing sectionthrough which can be seen position-indicating numbers marked on theunderlying portion of the front assembly, which is fixedly secured tothe base, the number visible being indicative of the position of thewiper on the resistance element. To provide further universality, thiscovering disc is keyed to a rotatable drive member extending through thecenter of the numbered stationary portion of the front, which has asuitable marker giving a similar, but less convenient, visual indicationof wiper position when the disc is omitted, for uses where space andcost are to be minimized.

These, and additional constructional features and advantages of theinvention, will best be understood by reference to the followingdetailed description taken in connection with the accompanying drawingsin which:

FIGURE 1 is a top or front view, with a portion partially broken away,of a potentiometer embodying one form of the invention (it will ofcourse be understood that top and front are substantiallyinterchangeable in description of structures of this type, because ofthe variety of orientations encountered in use);

FIGURE 2 is a sectional view taken along line 2-2 of FIGURE 1;

FIGURE 3 is a sectional view taken along line 33 of FIGURE 2, showingthe base assembly in elevation;

FIGURE 4 is a bottom or rear view of an insulating coupling memberconstituting a portion of the potentiometer;

FIGURE 5 is a top plan view of the base structure prior to assembly withthe front;

FIGURE 6 is a top plan view of a conducting coupling member used on thewiper assembly;

FIGURE 7 is a side elevational view of the member of FIGURE 6; and

FIGURE 8 is a side elevational view, partially broken away in section,of another assembly utilizing the invent1on.

In FIGURES 1 through 7 there is shown one form of potentiometer 10 whichincludes a unitary base assembly 11. Base assembly 11 includes a hollowcylindrical base 12 of suitable insulating material. Housed within base12 are a resistance element 13 and a wiper assembly 14, both mounted inthe base in a permanent manner, as will be described hereinafter. Fromthe resistance element and wiper assembly there extend three terminalmembers 15 (only two of which are visible in FIGURE 2) which protrudethrough the bottom or rear wall of base 12. The terminal member set asshown is of the type which may plug directly into suitable mountingsockets such as used in printed circuits. Covering the front end ofpotentiometer 10 is a rotatable outer disc 16 with serrations 17 aboutits periphery and with a suitable screwdriver-receiving slot 18substantially centrally located in its surface.

The base 12, shown in its unassembled state in FIGURE 5, has on itsinner face a generally cup-shaped recess 20 having around the bottom anannular ledge 22 which extendsto the sidewall 24 and serves as themounting support for resistance element 13. Inwardly of the ledge 22 isan annular channel 25. In the center is a circular raised floor or boss26. p In a small angular sector floor 26 continues radially outwardly ina rib 27 blocking the channel. At the center of floor 26, there isprovided a circular opening 28 within which is tightly fitted a centralterminal 29, as can be seen best in FIGURES 1 and 2. Terminal 29 is oneof the terminals of set 15, the other terminals 30 and 31 extending intoterminal wells or enlargements 32 and 33 in channel 25.

Within the base 12 there is positioned an annular resistance element 13.The resistance element shown may be wire wound about a mandrel 35 toencompass a functional angle of 300 degrees or more and with its endssoldered to terminals 30 and 31. The resistance element is positionedand suitably secured within the base so that the open region between itsends is diametrically opposite the rib 27 in the channel 25, the purposeof which will be described later.

The center terminal 29 serves as a pintle or bearing about which wiperassembly 14 is pivoted and also serves the function for which a slipring is normally provided in conventional constructions. This terminal29 protrudes from the central floor area 26 to a height suflicient toaccommodate the components of wiper assembly 14. The bottom component ofthis wiper assembly is a metallic flat washer 36 which rests on floor 26surrounding the terminal 29. Abutting against washer 36, alsosurrounding terminal 29, there is positioned a bowed or arched biasspring 38. Wiper assembly 14 further includes, abutting bias spring 38,a coupling plate 40 which is generally circular, with an opening passingthe center terminal 29. Extending integrally from the outer periphery ofthe coupling plate in the forward or upward direction away from floor 26are four equally spaced coupling lugs 42. These lugs form substantiallyright angles with the coupling plate proper, are mutually parallel andare symmetrically disposed about the center terminal 29. Be-

tween one pair of adjacent lugs 42, the coupling plate includes a stoparm 44 which is formed to extend radially outwardly and thensubstantially perpendicularly into channel 25. This arm strikes rib 27to form endstops for the wiper assembly in both directions at or nearthe contacting by the wiper of the respective ends of the resistanceelement.

A centrally flat wiper member 46 is locked to coupling plate 40 forrotation therewith. Wiper member 46 includes a generally circularcentral portion about the center terminal and a radially extendingresilient contacting or brush arm 48 of sufficient length to contact theresistance element and is formed with a longitudinal bend-line at itsouter end to pr,ovide a narrow region of contact with resistance element13. Extending radially from the wiper member central portiondiametrically opposed to the contacting arm 48 in the plane of the wipermember is an aligning arm 50 secured to stop arm 44, as by spotwelding.

Wiper assembly 14 is completed by the addition of a flat washer 52forwardly adjacent to the wiper member, against which the forward end ofterminal member 24 is swaged or flared as indicated at 54 to hold allthe members of the wiper assembly between flared end 54 of the terminalmember 29 and the floor 26. Withinwiper assembly 14, the arched spring38 exerts axial biasing 4 stop arm 44 to establish extreme rotarypositions at the ends of the element.

The base assembly as described may be used with any one of a largenumber of driving member assemblies or fronts. In the form of theinvention shown in FIG- URES l to 7, the coupling plate 40 is engaged indriven relation with an insulating coupling 60, preferably molded of asuitable plastic, having a circular surface 62 adjacent to couplingplate 40. In surface 62, as shown in FIGURE 4, there are provided a setof four sockets or wells 63, spaced to receive the lugs 42, the regionsbetween the wells being somewhat bevelled or conical. These wells andtheir mating lugs are spaced a radial distance from the axis of rotationof the wiper assembly much greater than the radius of the terminal 29 toprovide cooperating or keyed parts large enough to allow easy manualhandling in assembly. Thisfeature is of special importance in miniatureprecision potentiometers which have an outer diameter of of an inch orless.

Suitable adhesive sealing materials (not shown) may be set into wells 63to insure permanent and continuous engagement of the lugs 42 with thecoupling 60. To provide clearance for end 54 of terminal 29, surface 62is recessed at its center as indicated at 67 (FIGURE 2). The form of theinvention shown in FIGURES l and 2 utilizes on the outer surface 65 ofcoupling 60 a slot 64. Slot 64 is sized to accept a screwdriver-likeblade 66 extending inwardly from the outer covering disc 16 and securedin the slot 64 by an adhesive as the final step of assembly, and beingitself provided with a screwdriver slot 18.

The perimeter 72 of the forward portion of coupling 60 is formed with ashoulder seating an O-ring 74 which in turn fits snugly within ametallic outer cup-shaped housing 76. This O-ring serves to effectivelyseal the interior against moisture. The metal outer or front housing 76includes a tubular sidewall 78 having a shoulder 79 seating the lip ofthe base. The front housing or shell 76 has at its front end an annularinwardly directed flange 80 surrounding a circular opening 81 throughwhich the comparatively small outer end 65 of the coupling 60 rotatablyfits. To complete the assembly of cup-shaped housing shell 76 to base12, the rear end of the shell may be spun over against the base rearwall, or suitably sealed to the base by adhesives as illustrated inFIGURE 2, the rear edge of the base having a bevel at 82 for suchfastening. v

Shown also in FIGURE 1 is a viewing window 84 through the thickness ofdisc 16. As the disc is rotated with respect to the outer housing 76,window 84 passes over the surface flange 80 of the outer housing andexposes numbers inscribed on the flange face to indicate the position ofthe rotor or wiper assembly, the angular width of the window beinggreater than the spacing between numbers to permit visual interpolation.It will be observed that the framing of the calibration markings thusprovided makes reading of the setting extremely easy, and thatadjustment is readily made either by the convenient thumb wheel type ofknob thus provided or by means of a screwdriver. With this construction,the general utility of the device is greatly aided; where thepotentiometer is installed in a relatively inaccessible location where ascrewdriver must be employed, the difficulty of reading normallyassociated with such locations is greatly eased by the window type ofindicator, the reading of which is further facilitated by a liner 85inscribed with easily visible marker lines. Where economy and space arepredominant factors, the outer disc 16 may be omitted, and theadjustment made by screwdriver or wrench insertion in the slot 64,reading of position being ,into the interior. This function is served bythe outer disc 16 in the illustrated embodiment, the periphery of thedisc being in close sliding relation to the flange 80 of thehousingg'this relation is easily obtained without precision tolerancesin manufacture by simply pressing these surfaces into firm slidingcontact in the final assembly operation of insertion of the blade 66into the adhesive (not shown) in the slot 64.

It will be noted that the diameter of surface 62 of coupling 60 isgreater than that of opening 81 in flange 80 so that the coupling isfirmly held against axial movement when the O-ring 74 is utilized andhousing 76 is locked to the base.

Now turning to FIGURE 8, there is shown another potentiometer 90 of theminiature precision type having a conventional type of shaft 92. In thedetails of its inner construction potentiometer 90 closely resemblespotentiometer 10. Potentiometer 90 includes a base assembly 11 identicalto that described for the embodiment described above, including a base12, a resistance element '13 and a wiper assembly 14. Protruding fromwiper assembly 14 toward the drive shaft is a coupling plate 40identical to the coupling plate previously described with its extendinglugs 42. For engagement with this coupling plate and its lugs, the formof the invention shown in FIGURE 8 utilizes an insulating coupling plate94 which has a face 96 with suitable openings or wells 98 engaging thelugs 42. The face 96 of the engaging plate 94 is identical inconfiguration with that of engaging structure 60.

On its surface opposite face 96, plate 94 includes an annular projection100 which is fitted in suitable fashion to shaft 92 to forman integralunit. The shaft 92 is fitted rotatably within a threaded mountingbushing 102 of cup-shaped housing 103. Housing 103 includes a frontcover plate 104 which covers the base interior and further includes atubular sidewall 105 which fits about the base structure 12 and has itsrearward edge affixed to the rear wall of the base as. shown at 106 (thespinning-over of the rearward edge previously mentioned beingillustrated in this case) to complete the assembly.

A set of terminals 108 extend from the base. This terminal set as shownin FIGURE 8 is of the type designed for the soldering of connectingleads in this instance.

Potentiometer 90 is of the bushing-mounted type in V which theshaft-bearing bushing 102 is mounted in a suitable opening by the use ofnuts 110 and having a conventional forwardly extending keying pin (notshown) to prevent rotation in the mounting panel. It will be noted thatthe coupling plate 94 in this instance slides against the inside ofcover plate 104 and acts to prevent axial movement of shaft 92. As inthe previous case, great precision in manufacture of the parts toprovide exact fit may be avoided by assembly of the portionsconstituting the front to the universa base before complete setting ofthe adhesive in the wells 98; to accommodate tolerances achieved withoutgreat expense, the wells, as illustrated, are slightly greater than ahalf-circle of a diameter slightly larger than the width of the lugs 42,the latter and their supporting plate being desirably formed of a softberyllium copper alloy to permit slight deformation; although adhesiveis desirably used in this joint, the fit and accommodation may easily bemade adequate to assure proper alignment without the use of adhesive,with no backlash problem created except in uses involving anextraordinary number of readjustments of position during the lifetime ofthe equipment in which the potentiometer is to be installed. Substantialtolerances in longitudinal dimensions are permissible even in very tinystructures without requiring excessive care in assembly, and with aminimum of mechanical parts, all of relatively low cost. No lockingrings or other stops for axial motion of the drive member are required.Because of the illustrated construction of the unitary base assembly,excessive inward thrust on the shaft in use of the device, as in lack ofcare in making a screwdriver adjustment, merely results in temporarydeformation of the spring 38, the recessing of the drive member at 67preventing the application of any force to the center terminal (servingas slip ring and rotational bearing) which might deform it in a mannerto interfere with the electrical contact with the wiper assembly. Thebevelled or conical shape of the insulating coupling member in theregion of the wiper contact accommodates corresponding temporary bendingback of the contact arm without in ury.

It can be seen that either base assembly as described herein (differingonly in the terminals) is capable of being mounted or assembled to manyforms of driving members of which only two have been shown, and withmany front housing configurations. Precision potentiometers of adiameter of a half-inch or less are thus easily and inexpensivelyfabricated in a variety of forms.

While there have been described what are at present thought to be themost preferred forms of the invention, it may be understood thatmodifications may be made therein and the patent protection afforded theinvention shall accordingly be determined in accordance with thestructures as described in the appended claims, and equivalents thereof.

What is claimed is:

1. A potentiometer comprising a circular housing, a resistance elementand a wiper contact within the housing, and an operating member coupledto the Wiper contact and extending centrally from the face of thehousing, said potentiometer having:

(a) spaced position calibration markings inscribed on the face of thehousing surrounding the operating member, and

(b) a circular manipulating knob on the outer end of the operatingmember, substantially coextensive with the face of the housing andclosely overlying the calibration markings in sliding relation with theface of the housing,

(0) the knob having a window opening exposing in its successiverotational positions only the portion of the calibration markingscorresponding to the respective positions, the window opening being ofangular width greater than the spacing between markings.

2. A potentiometer as described in claim 1 characterized by:

(d) the knob being in keyed engagement with the portion of the operatingmember extending through the housing substantially at the outer surfaceof the housing, I l

(e) said portion itself having an indicator adapted for reading ofposition in cooperation with the calibration markings.

3. A potentiometer comprising:

(a) a circular insulating base having interior and exterior sides,

(b) a resistance element mounted on the interior side of the base,

(0) a rigid conducting terminal extending centrally through the base andfixedly mounted therein and having its inner end extending from theinterior s1 e,

(d) a wiper entirely of conductive materials having a first portioncontacting the resistance element and a second portion mounted forrotation on, and in electrical contact with, the portion of the terminalwithin the interior,

(e) a front housing enclosing the interior side of the base and meansmounted entirely on the base for retaining said wiper in position on thebase,

(1) an external operating member extending through the front housing,

(g) an insulating coupling between the wiper and the operating member,

(h) the insulating coupling including a pair of members of largerdiameter than the terminal and having mutually interengaging rotationalcoupling elements thereon,

(i) one of the members ofsaid pair having a plurality of axiallyextending prongs and'the other having recesses registering therewith,

(j) the front housing having a central aperture of smaller diameter thanthe members of said coupling pair, and the forward member of saidcoupling pair being confined in axial position by the portionsurrounding the aperture and having a forwardly extending portion in theaperture,

(k) the rearward member of said pair being affixed to the wiper andhaving a rearwardly extending portion, and

(l) the base having a fixed stop portion in the rotational path of saidrearwardly extending portion fixing the rotational limits of the wiperpath.

4. The potentiometer of claim 3 further characterized (m) the frontsurface of the front housing having calibration markings thereonsurrounding the portion of the operating member extending therethroughand the operating member having a portion overlying the markings andhaving a viewing window therethrough, for indication of the rotationalposition of the wiper.

5. A potentiometer comprising:

(a) a circular insulating base having interior and exterior surfaces andhaving a central conducting terminal and two otherconducting terminalsextending therethrough in the axial direction,

(b) a resistance element mounted on the interior surface of the baseoutwardly spaced from the central terminal to form an annular regiontherebetween and having the ends thereof electrically connected to saidother terminals,

() a rotary wiper assembly having a radial wiper portion engaging theresistance element and having a portion extending in the axial directioninto the annular region,

(d) a fixed stop member on the base in said annular region spaced in theaxial direction from the path of the radial wiper portion but engagingsaid axially extending portion of the rotary wiper assembly to limit therotation thereof,

(e) means on the inner-end of 'the central terminal 7 for mounting thewiper assembly thereon in conductive rotary contact therewith,

(f) a cup-shaped front housing enclosing the interior surface of thebase,

(g) an external operating member extending centrally through the fronthousing, and

(h) mating members on the Wiper assembly and the operating membercoupling them for rotational motion. 1

6. The potentiometer of claim 5 characterized by:

(i) the wiper assembly comprising a substantially rigid conductingmember having a body portion surrounding the central terminal and havingan integrally formed tab extension extending in one axial direction intosaid annular region to engage the fixed stop member and havingintegrally formed prongs extending in the opposite axial direction tomate with the drive member.

7. A potentiometer comprising:

(a) an insulating base having interior and exterior surfaces, I

(b) a resistance element and a rotary wiper mounted on the interiorsurface of the base,

(0) a metallic tubular front housing member enclosing the interiorsurface of the insulating base and having an inwardly extending flangeon the front end thereof defining an aperture,

(d) an insulating drive member within the housing 25 coupled to thewiper and having an outer portion rotatable in the apertureand an innerportion underlying the flange,

(e) a knob member secured in mating engagement with the outer portion ofthe drive member and having a periphery substantially coextensive withthe end of the front housing member and in sliding engagement with theflange,

(f) spaced visual position indicia on the flange, and

(g) a window in the knob member for viewing of the indicia on theflange, the window being of angular width greater than the spacingbetween calibration markings.

References Cited in the file of this patent UNITED STATES PATENTS347,120

Barden et a1. Oct. 20, 1959

1. A POTENTIOMETER COMPRISING A CIRCULAR HOUSING, A RESISTANCE ELEMENTAND A WIPER CONTACT WITHIN THE HOUSING, AND AN OPERATING MEMBER COUPLEDTO THE WIPER CONTACT AND EXTENDING CENTRALLY FROM THE FACE OF THEHOUSING, SAID POTENTIOMETER HAVING: (A) SPACED POSITION CALIBRATIONMARKINGS INSCRIBED ON THE FACE OF THE HOUSING SURROUNDING THE OPERATINGMEMBER, AND (B) A CIRCULAR MANIPULATING KNOB ON THE OUTER END OF THEOPERATING MEMBER, SUBSTANTIALLY COEXTENSIVE WITH THE FACE OF THE HOUSINGAND CLOSELY OVERLYING THE CALIBRATION MARKINGS IN SLIDING RELATION WITHTHE FACE OF THE HOUSING, (C) THE KNOB HAVING A WINDOW OPENING EXPOSINGIN ITS SUCCESSIVE ROTATIONAL POSITIONS ONLY THE PORTION OF THECALIBRATION MARKINGS CORRESPONDING TO THE RESPECTIVE POSITIONS, THEWINDOW OPENING BEING OF ANGULAR WIDTH GREATER THAN THE SPACING BETWEENMARKINGS.